NHibernate mapping of lookup collection (if that makes any sense)

Book.cs
int BookID
string Title
List<BookTag> Tags

Tag.cs
int TagID
string Title

BookTag.cs
int ID
int BookID
int TagID

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="DomainModel" namespace="DomainModel.Books">
  <class name="DomainModel.Books.Book" table="Books">
    <id name="BookID" type="Int32" unsaved-value="0">
      <generator class="native"/>
    </id>
    <property name="Title" type="String" not-null="true"/>
    <set lazy="true" name="Tags" table="BookTags" generic="true" inverse="true" cascade="delete">
      <key column="BookID"/>
      <one-to-many class="DomainModel.Books.BookTag, DomainModel"/>
    </set>
  </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="DomainModel" namespace="DomainModel.Books">
  <class name="DomainModel.Books.BookTag" table="BookTags">
    <id column="BookTagID" name="BookTagID" type="Int32" unsaved-value="0">
      <generator class="native"/>
    </id>
    <many-to-one name="Tag">
      <column not-null="true" name="TagID"/>
    </many-to-one>
    <many-to-one name="Book">
      <column not-null="true" name="BookID"/>
    </many-to-one>
  </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="DomainModel" namespace="DomainModel.Books">
  <class name="DomainModel.Books.Book" table="Books">
    <id name="BookID" type="Int32" unsaved-value="0">
      <generator class="native"/>
    </id>
    <property name="Title" type="String" not-null="true"/>
    <bag name="Tags" table="BookTag" generic="true">
      <key column="BookID" on-delete="noaction"></key>
      <many-to-many class="Tag" column="TagID"></many-to-many>
    </bag>
  </class>
</hibernate-mapping>